Abstract:

An access control apparatus of a data storage device includes a first
connecting unit configured to be removably connected with a power supply
device, perform data transmission through a first data-transmission line,
and be supplied with power through a first power-transmission line, a
second connecting unit configured to be removably connected with the data
storage device, perform data transmission through a second
data-transmission line, and supply power through a second
power-transmission line, a data transfer processing unit configured to
perform data transfer between the power supply device and the data
storage device, a power consumption measuring unit configured to measure
power supplied from the power supply device through the first
power-transmission line, and a power-transmission capability monitoring
unit configured to control the data transfer processing unit in
accordance with power consumption measured by the power consumption
measuring unit.

Claims:

1. An access control apparatus of a data storage device, comprising:a
first connecting unit configured to be removably connected with a power
supply device, perform data transmission through a first
data-transmission line, and be supplied with power through a first
power-transmission line;a second connecting unit configured to be
removably connected with the data storage device, perform data
transmission through a second data-transmission line, and supply power
through a second power-transmission line;a data transfer processing unit
configured to perform data transfer between the power supply device and
the data storage device;a power consumption measuring unit configured to
measure power supplied from the power supply device through the first
power-transmission line; anda power-transmission capability monitoring
unit configured to control the data transfer processing unit in
accordance with power consumption measured by the power consumption
measuring unit; whereinthe data transfer processing unit includes a test
data communication unit that performs transmission of test data to the
power supply device through the first data-transmission line while
changing power load in multiple stages, in a manner to be free from
supplying power to the data storage device, andthe power-transmission
capability monitoring unit includes a storing unit that stores a maximum
power-transmission power at which the test data communication unit can
perform data transmission at a highest power load, in response to a
measurement result of the power consumption measuring unit, and controls
the data transfer processing unit such that the data transfer processing
unit starts data transfer between the power supply device and the data
storage device and temporarily stops an access to the data storage device
in a period during which power consumption measured by the power
consumption measuring unit exceeds the maximum power-transmission power
stored in the storing unit.

2. The access control apparatus of a data storage device according to
claim 1, wherein the power-transmission capability monitoring unit allows
the data transfer processing unit to control a data transfer speed
between the power supply device and the data storage device so as to
prevent power consumption measured by the power consumption measuring
unit from exceeding the maximum power-transmission power stored in the
storing unit.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to an access control apparatus of a
data storage device. The access control apparatus controls an access to
the data storage device which is removably connected thereto.

[0003]2. Description of the Related Art

[0004]An access control apparatus for controlling an access to a data
storage device which is removably connected thereto commonly supplies
power to the data storage device to drive the data storage device.
Therefore, power consumption of the access control apparatus changes
depending on an operation of the data storage device.

[0005]Here, examples of the access control apparatus include an access
control apparatus of a bus-power type and an access control apparatus of
a self-power type (Japanese Unexamined Patent Application Publication No.
2004-86359). The access control apparatus of the bus-power type operates
by using supply current of a bus-power supply device which is connected
thereto through a signal cable such as a USB and an IEEE1394. The access
control apparatus of the self-power type operates by using self power
such as an AC adapter and an auxiliary battery.

[0006]The access control apparatus of the bus-power type which is designed
to be used within an acceptable range of a bus power specification can
operate only by connecting a signal cable to a bus-power supply device.
Therefore, the access control apparatus of the bus-power type can be used
outdoors or in a place having a difficulty in securing electric power,
thus providing higher degree of freedom of a utilization place, compared
to the access control apparatus of the self-power type which uses an AC
adapter, an auxiliary battery, or the like.

SUMMARY OF THE INVENTION

[0007]However, in a case where an added value of power consumption of the
access control apparatus of the bus-power type and power consumption of
the data storage device which is connected to the access control
apparatus exceeds the maximum power supply capability of the bus-power
supply device, the following problem arises. Namely, in this case, power
for operating the access control apparatus runs short, causing an
abnormal operation or destruction of data stored in the data storage
device.

[0008]To avoid such problem, there are a method in which an auxiliary
power such as a battery is added and a method in which bus-power is
switched to self-power. However, these methods do not realize space
saving and simple wiring, limiting the degree of freedom of an
installation space and a utilization place which are advantageous points
of the apparatus of the bus-power type.

[0009]It is true that there is a case where more value of current than a
specified value may be supplied depending on a mounting state of the
bus-power supply device. However, the access control apparatus does not
grasp the maximum bus-power supply capability, so that the access control
apparatus has not used power at a specified value or more even in an
environment in which the apparatus normally operates at power consumption
of the specified value or more.

[0010]Further, it has been difficult for the access control apparatus to
grasp power consumption thereof because power consumption of the data
storage device which is removably connected thereto changes depending on
a storage capacity, an accessible speed, and the like. Thus, in a case
where the power consumption exceeds a bus power supply limit, a defect of
the access control apparatus which is not recognized by the bus-power
supply device arises or data of the data storage device is destroyed.

[0011]It is desirable to provide an access control apparatus of a data
storage device. The access control apparatus is securely capable of
performing data transfer between a power supply device and the data
storage device within power which can be supplied from the power supply
device.

[0012]An access control apparatus of a data storage device, according to
an embodiment of the present invention, includes a first connecting unit
configured to be removably connected with a power supply device, perform
data transmission through a first data-transmission line, and be supplied
with power through a first power-transmission line, a second connecting
unit configured to be removably connected with the data storage device,
perform data transmission through a second data-transmission line, and
supply power through a second power-transmission line, a data transfer
processing unit configured to perform data transfer between the power
supply device and the data storage device, a power consumption measuring
unit configured to measure power supplied from the power supply device
through the first power-transmission line, and a power-transmission
capability monitoring unit configured to control the data transfer
processing unit in accordance with power consumption measured by the
power consumption measuring unit. In the access control apparatus of a
data storage device, the data transfer processing unit includes a test
data communication unit that performs transmission of test data to the
power supply device through the first data-transmission line while
changing power load in multiple stages, in a manner to be free from
supplying power to the data storage device. Further, in the access
control apparatus, the power-transmission capability monitoring unit
includes a storing unit that stores a maximum power-transmission power at
which the test data communication unit can perform data transmission at a
highest power load, depending on a measurement result of the power
consumption measuring unit, and controls the data transfer processing
unit such that the data transfer processing unit starts data transfer
between the power supply device and the data storage device and
temporarily stops an access to the data storage device in a period during
which power consumption measured by the power consumption measuring unit
exceeds the maximum power-transmission power stored in the storing unit.

[0013]In the embodiment of the present invention, an operation of the data
transfer processing unit is controlled to start the data transfer between
the power supply device and the data storage device, and temporarily stop
an access to the data storage device in a period during which power
consumption measured by the power consumption measuring unit exceeds the
maximum power-transmission power stored in the storing unit. Thus, in the
embodiment of the present invention, an access to the data storage device
is controlled based on the maximum power-transmission power. Accordingly,
the access control apparatus can stably operate within power which can be
supplied from the power supply device and securely perform the data
transfer between the power supply device and the data storage device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 illustrates the whole configuration of a data transfer system
in which an access control apparatus of a data storage device according
to an embodiment of the present invention is built;

[0015]FIG. 2 is a flowchart for explaining specific data transfer
processing performed by a removable media control apparatus;

[0016]FIG. 3 is a flowchart for explaining the specific data transfer
processing performed by the removable media control apparatus;

[0017]FIGS. 4A to 4D are timing diagrams for explaining an operative
example of data transfer processing;

[0018]FIGS. 5A and 5B are timing diagrams for explaining correction
processing by which power-transmission capability is corrected in a case
where data transfer between a host device and a removable media is
normally completed;

[0019]FIGS. 6A and 6B are timing diagrams for explaining correction
processing by which power-transmission capability is corrected in a case
where the data transfer between the host device and the removable media
is not normally completed;

[0021]FIG. 8 is a diagram for explaining processing in which data transfer
is realized at as high-speed as possible while preventing power load from
exceeding the maximum power-transmission capability; and

[0022]FIGS. 9A and 9B are timing diagrams for explaining the processing in
which data transfer is realized at as high-speed as possible while
preventing power load from exceeding the maximum power-transmission
capability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023]An embodiment of the present invention will now be described with
reference to the accompanying drawings. It should be understood that the
present invention is not limited to the embodiment described below and
various modifications and alterations may occur within the scope of the
invention.

[0024]An access control apparatus of a data storage device according to
the embodiment of the present invention is an apparatus for controlling
an access to a data storage device which is removably connected to the
apparatus. Such an access control apparatus is applied as a removable
media control apparatus 1 shown in FIG. 1, for example, and is built to
be used in a data transfer system 100 that performs data transfer between
a host device 2 and a removable media 3. The description is offered in
the following order.

1. Whole Configuration

2. Data Transfer Processing

3. Operative Example

1. Whole Configuration

[0025]The removable media control apparatus 1 corresponds to an access
control apparatus of a data storage device according to the embodiment of
the present invention and is removably connected with the host device 2
and the removable media 3.

[0026]The host device 2 is a power supply device which is removably
connected with the removable media control apparatus 1 through a
communication interface cable 2a such as a USB and an IEEE1394 capable of
supplying bus power. The host device 2 supplies bus power to the
removable media control apparatus 1 through the communication interface
cable 2a so as to operate the removable media control apparatus 1.
Further, the host device 2 transmits and receives data to and from the
removable media control apparatus 1 through the communication interface
cable 2a.

[0027]The removable media 3 is a removable data storage device such as a
removable hard disk drive, a micro drive, or a memory card. The removable
media 3 is connected with the removable media control apparatus 1 through
a communication interface 3a capable of supplying power. The removable
media 3 operates by receiving power supply from the removable media
control apparatus 1. Further, a storage region of the removable media 3
is accessed by the removable media control apparatus 1 and thus the
removable media 3 transmits and receives data to and from the host device
2 through the removable media control apparatus 1.

[0028]In the data transfer system 100 configured as described above,
specific configuration and operation of the removable media control
apparatus 1 are focused to be described below.

[0029]The removable media control apparatus 1 includes a host device
connecting unit 11 connecting with the host device 2 and a removable
media connecting unit 12 connecting with the removable media 3. The
removable media control apparatus 1 further includes a data transfer
processing unit 13 that performs data transfer, a power consumption
measuring unit 14 that measures power consumption, and a
power-transmission capability monitoring unit 15 that controls an
operation of the data transfer processing unit 13 in response to a
measurement result of the power consumption measuring unit 14.

[0030]The host device connecting unit 11 is removably connected with the
host device 2 through the communication interface cable 2a. Specifically,
the host device connecting unit 11 transmits and receives data to and
from the host device 2 through a data-transmission line 21 which is
provided in the communication interface cable 2a. Further, the host
device connecting unit 11 is supplied with bus power from the host device
2 through a power-transmission line 22 which is provided in the
communication interface cable 2a and the power consumption measuring unit
14 which will be described later.

[0031]The removable media connecting unit 12 is removably connected with
the removable media 3 through the communication interface 3a.
Specifically, the removable media connecting unit 12 includes a
communication interface unit 121 and a media power controlling unit 122.
The communication interface unit 121 transmits and receives data to and
from the removable media 3 through a data-transmission line 31 which is
provided in the communication interface 3a. The media power controlling
unit 122 supplies bus power to the removable media 3 through a
power-transmission line 32 provided in the communication interface 3a, in
accordance with a control command from the power-transmission capability
monitoring unit 15 which will be described later.

[0033]Further, the data transfer processing unit 13 includes a test
communication processing unit 131 that performs test communication with
the host device 2 in accordance with a control command from the
power-transmission capability monitoring unit 15 which will be described
later. The test communication processing unit 131 performs communication
using dummy data as test data with the host device 2 while changing power
load in multiple stages, in a manner to supply no power to the removable
media 3, as specifically described later.

[0034]The power consumption measuring unit 14 is connected with the
power-transmission line 22 provided in the communication interface cable
2a and supplies power which is supplied from the host device 2 to each
unit of the removable media control apparatus 1. Here, power supplied
from the host device 2 changes in accordance with an operating state of
the removable media control apparatus 1 and the removable media 3, so
that the power consumption measuring unit 14 measures an added value of
power consumed by the removable media control apparatus 1 and power
consumed by the removable media 3. Then, the power consumption measuring
unit 14 informs the consumption power which is measured thereby to the
power-transmission capability monitoring unit 15.

[0035]The power-transmission capability monitoring unit 15 has the
following configuration in order to control an operation of the data
transfer processing unit 13 in accordance with the power consumption
measured by the power consumption measuring unit 14. Namely, the
power-transmission capability monitoring unit 15 includes a
power-transmission capability register 151 and a comparing unit 152. The
power-transmission capability register 151 stores the maximum
power-transmission power at which the test communication processing unit
131 can perform data transmission in a state of the highest power load.
The comparing unit 152 compares power consumption measured by the power
consumption measuring unit 14 to the maximum power-transmission power.

[0036]The power-transmission capability monitoring unit 15 controls the
data transfer processing unit 13 to start data transfer between the host
device 2 and the removable media 3 and, depending on a comparison result
of the comparing unit 152, temporarily stop an access to the removable
media 3 in a period during which the power consumption exceeds the
maximum power-transmission power.

[0037]The removable media control apparatus 1 having the above-mentioned
configuration controls an access to the removable media 3 based on the
maximum power-transmission power acquired by the test communication
processing. By such processing, the removable media control apparatus 1
stably operates within power which can be supplied from the host device 2
and can securely perform data transfer between the host device 2 and the
removable media 3.

2. Data Transfer Processing

[0038]Specific data transfer processing performed by the removable media
control apparatus 1 is now described with reference to FIG. 2. Here, it
is assumed that the removable media control apparatus 1 operates by power
supplied from the power-transmission line 22 which is provided to the
communication interface cable 2a. Further, it is assumed that the
removable media control apparatus 1 is in a state supplying no power to
the removable media 3 which is connected therewith through the
communication interface 3a.

[0039]In step S11, the power-transmission capability monitoring unit 15
sets power supplied from the host device 2 to be a specified value
communicable through the data-transmission line 21, and thus establishes
a connection between the host device 2 and the data transfer processing
unit 13. Here, the communicable specified value is a value showing bus
power which is minimally allowed for maintaining communication which
follows a predetermined communication specification. Then the
power-transmission capability monitoring unit 15 controls the test
communication processing unit 131 to perform test communication with the
host device 2.

[0041]In step S13, the test communication processing unit 131 determines
whether an error occurs in the data communication of dummy data with the
host device 2 or not. When the communication error does not occur, the
process goes to step S14. When the communication error occurs, the
process goes to step S15.

[0042]In step S14, the power-transmission capability monitoring unit 15
increases power-transmission capability power of the host device 2 by 10%
and stores the increased power value in the power-transmission capability
register 151 as information showing the maximum power-transmission power.
In specific, the test communication processing unit 131 increases
communication load by test data used in test communication with the host
device 2 so as to increase a power-transmission capability value from the
host device 2. Then, the process goes back to step S12.

[0043]In step S15, the power-transmission capability monitoring unit 15
determines whether a current power-transmission capability value of the
host device 2 is smaller than the specified value set in step S11 or not.
Here, when the power-transmission capability value is smaller than the
specified value, the process goes to step S16. When the
power-transmission capability value is not smaller than the specified
value, the process goes to step S17.

[0045]In step S17, the removable media control apparatus 1 supplies power
to the removable media 3 so as to drive the removable media 3 and start
data transfer between the host device 2 and the removable media 3. Then,
the process goes to step S18.

[0046]In step S18, the data transfer processing unit 13 determines whether
a communication error occurs in the data transfer between the host device
2 and the removable media 3 or not. When the communication error does not
occur, the process goes back to step S12. When the communication error
occurs, the process goes to step S19.

[0049]In step S21, the test communication processing unit 131 determines
whether a communication error occurs in the data communication between
the host device 2 and the removable media 3 or not. When the
communication error occurs, the process goes back to step S19. When the
communication error does not occur, the process goes back to step S15.

[0050]Next, the processing according to step S17 is specifically described
with reference to FIG. 3.

[0051]In step S31, the removable media connecting unit 12 repeatedly
determines whether the removable media 3 is connected or not until the
connection is confirmed. After that, the process goes to step S32.

[0053]In step S33, the data transfer processing unit 13 determines whether
data transfer in an amount corresponding to the number of request data
transmitted from the host device 2 is completed or not. When the data
transfer is completed, the transfer processing is ended. When the data
transfer is not completed, the process goes to step S34.

[0054]In step S34, the removable media connecting unit 12 determines
whether the removable media 3 is connected or not. When the connection is
confirmed, the process goes to step S35. When the connection is not
confirmed, the transfer processing is ended.

[0055]In step S35, the data transfer processing unit 13 performs data
transfer of one packet which is the minimum transmission data unit
between the host device 2 and the removable media 3. Then, the process
goes to step S36.

[0056]In step S36, the power-transmission capability monitoring unit 15
compares power consumption measured by the power consumption measuring
unit 14 to the maximum power-transmission power stored in the
power-transmission capability register 151, with the comparing unit 152
thereof. Then, when the power consumption does not exceed the maximum
power-transmission capability, the process goes back to step S33. When
the power consumption exceeds the maximum power-transmission capability,
the process goes to step S37.

[0057]In step S37, the data transfer processing unit 13 temporarily stops
the data transfer processing so as to decrease the power load. Then, the
process goes to step S38.

[0058]In step S38, the power-transmission capability monitoring unit 15
compares power consumption measured by the power consumption measuring
unit 14 to the maximum power-transmission power stored in the
power-transmission capability register 151, with the comparing unit 152
thereof. Then, this step is repeated until the power consumption falls
below the maximum power-transmission capability, and then the process
goes to step S39 when the power consumption does not exceed the maximum
power-transmission capability.

[0060]Through the above-described processing process, the removable media
control apparatus 1 controls an operation of the data transfer processing
unit 13 so as to temporarily stop an access to the removable media 3 in a
period during which power consumption measured by the power consumption
measuring unit 14 exceeds the maximum power-transmission power stored in
the power-transmission capability register 151. Thus, the removable media
control apparatus 1 controls an access to the removable media 3 based on
the maximum power-transmission power, so that the removable media control
apparatus 1 can stably operate within power which can be supplied by the
host device 2 and securely perform the data transfer between the host
device 2 and the removable media 3.

3. Operative Example

[0061]As an operative example of the data transfer processing described
above, such test communication processing is described that a status with
respect to a command for confirming a connecting state of a device
connected in accordance with the USB specification is used as dummy data
with reference to FIGS. 4A to 4D. Here, FIG. 4A is a timing diagram
showing power supplied from the power-transmission line 22 in the
communication interface cable 2a. FIG. 4B is a timing diagram showing a
communication state of the data-transmission line 21 of the communication
interface cable 2a. FIG. 4C is a timing diagram showing power supplied
from the power-transmission line 32 of the communication interface 3a.
FIG. 4D is a timing diagram showing a communication state of the
data-transmission line 31 of the communication interface 3a.

[0062]First, from time t0 to time t1 in FIG. 4A, dummy data communication
is performed in accordance with steps S11 to S13 on a condition of power
load of 2.5 W which is a specified value of power supplied from the host
device 2, so as to confirm that a power-transmission capability operation
equivalent of 2.5 W is normal.

[0063]Next, from time t1 to time t2 in FIG. 4A, dummy data communication
is performed in accordance with steps S12 to S14 on a condition of power
load equivalent to 2.75 W which is 110% of 2.5 W so as to confirm a
normal operation.

[0064]Subsequently, from time t2 to time t3 in FIG. 4A, dummy data
communication is performed in accordance with steps S12 to S14 on a
condition of power load equivalent to 3.00 W which is 120% of 2.5 W so as
to confirm a normal operation.

[0065]Then, from time t3 to time t4 in FIG. 4A, dummy data communication
is performed in accordance with steps S12 to S14 on a condition of power
load equivalent to 3.25 W which is 130% of 2.5 W so as to confirm a
normal operation.

[0066]Here, in a case where the test communication using dummy data is
abnormally ended at time t4 in FIG. 4A, the power-transmission capability
of the host device 2 does not satisfy power-transmission capability
equivalent to 3.25 W. Accordingly, an upper limit of the
power-transmission capability value is determined to be 3.00 W and is
stored in the power-transmission capability register 151. For example, in
a case where the test communication is abnormally ended at
power-transmission capability equivalent to 2.5 W which is the specified
value, it is determined that the power-transmission capability of the
host device 2 does not satisfy the specified value or has a small margin
of supply capability, in accordance with step S16.

[0067]Next, specific processing after the start of the data transfer
between the host device 2 and the removable media 3 is described with
reference to FIGS. 5A to 6B. Here, FIGS. 5A and 6A are timing diagrams
showing power supplied from the power-transmission line 22 in the
communication interface cable 2a. FIGS. 5B and 6B are timing diagrams
showing a communication state of the data-transmission line 21 of the
communication interface cable 2a.

[0068]Correction processing for correcting the power-transmission
capability in a case where the data transfer between the host device 2
and the removable media 3 is normally completed is described with
reference to FIGS. 5A and 5B.

[0069]Such correction processing is performed because the maximum
power-transmission capability changes depending on a change of a state of
an operation environment of the host device 2 and the removable media
control apparatus 1. The removable media control apparatus 1 redetects an
upper limit of the power-transmission capability in a period in which
there is no data-transfer request or at an error occurrence after the
data transfer, by such the correction processing. Thus, the removable
media control apparatus 1 can accurately update the maximum
power-transmission capability which is stored in the power-transmission
capability register 151 in response to an operating state.

[0070]It is assumed that the processing according to step S17 is performed
from time t20 to time t21 in FIG. 5A and the data transfer is normally
completed at power-transmission capability equivalent to 3.0 W.

[0071]From time t22 to time t23 in FIG. 5A, dummy data communication is
performed in accordance with steps S12 to S14 at a power load equivalent
to 3.25 W which is 130% of 2.5 W so as to confirm a normal operation.
Here, the following operation is described in an assumption that the data
transfer is normally completed.

[0072]From time t24 to time t25 in FIG. 5A, dummy data communication is
performed in accordance with steps S12 to S14 at a power load equivalent
to 3.50 W which is 140% of 2.5 W so as to confirm a normal operation.
Here, when the test communication using dummy data is abnormally ended,
the power-transmission capability of the host device 2 does not satisfy
the power-transmission capability equivalent to 3.50 W. Therefore, an
upper limit of the power-transmission capability value is determined to
be 3.25 W and is stored in the power-transmission capability register
151.

[0073]From time t26 to time t27 in FIG. 5A, data transfer is performed in
accordance with step S17 at a power load equivalent to 3.25 W, being able
to normally complete the transfer processing.

[0074]Correction processing for correcting the power-transmission
capability in a case where the data transfer between the host device 2
and the removable media 3 is not normally completed is described with
reference to FIGS. 6A and 6B.

[0075]It is assumed that processing in accordance with step S17 is
performed from time t30 to time t31 in FIG. 6A and the data transfer is
not normally completed at a power load equivalent to 3.25 W.

[0076]From time t32 to time t33 in FIG. 6A, dummy data communication is
performed in accordance with steps S19 to S21 at a power load equivalent
to 3.0 W which is 120% of 2.5 W so as to confirm a normal operation.

[0077]From time t34 to time t35 in FIG. 6A, data transfer is performed in
accordance with step S17 at a power load equivalent to 3.0 W, being able
to normally complete the transfer processing.

[0078]As is apparent from the above-described processing, the removable
media control apparatus 1 according to the embodiment of the present
invention is capable of performing an error response with respect to a
request of data communication to the removable media 3 which is more
likely abnormally ended due to power shortage.

[0079]In contrast, related art data transfer processing is described with
reference to FIGS. 7A to 7D. Here, FIG. 7A is a timing diagram showing
power supplied from a host device. FIG. 7B is a timing diagram showing a
communication state between the host device and a removable media control
apparatus. FIG. 7C is a timing diagram showing power supplied to the
removable media. FIG. 7D is a timing diagram showing a communication
state between the removable media control apparatus and the removable
media.

[0080]In the related art data transfer processing, it is assumed that the
removable media control apparatus receives power supplied from the host
device at time t10 in FIG. 7A, and then starts power supply to the
removable media at time tn. After that, data transfer using real data is
started at time t12 in the related art data transfer processing. However,
the removable media control apparatus does not grasp out
power-transmission capability of the host device. Therefore, when power
load is increased at the highest data transfer speed, power shortage
causes malfunction, causing data destruction.

[0081]As is apparent from a comparison with the related art example, the
removable media control apparatus 1 according to the embodiment of the
present invention can prevent data destruction caused by malfunction.

[0082]Further, the removable media control apparatus 1 performs the
transfer processing in accordance with step S33 to S39 and thus controls
the data transfer speed between the host device 2 and the removable media
3, being able to realize high-speed data transfer while preventing power
consumption from exceeding the maximum power-transmission power.

[0083]FIGS. 8 to 9B illustrate an operative example of processing in which
data transfer is realized at as high-speed as possible while preventing
power consumption from exceeding power load equivalent to 3.25 W which is
set to be the maximum power-transmission capability.

[0084]First, it is assumed that a transfer command of 64 KB with respect
to the removable media 3 is issued from the host device 2 in accordance
with step S32, at time t40 shown in FIGS. 8 and 9A. Then, from time t41
to time to shown in FIGS. 8 and 9A, power consumption is compared to the
maximum power-transmission capability of 3.25 W in each data transfer in
which 512 bytes are set to be 1 packet, in accordance with steps S35 to
S39.

[0085]At this time, the data transfer processing unit 13 performs data
communication in which the power consumption does not exceed the
power-transmission capability of 3.25 W while performing temporary stop
and restart of the data transfer in accordance with a control command
from the power-transmission capability monitoring unit 15.

[0086]For example, the power-transmission capability monitoring unit 15
uses the comparing unit 152 thereof to compare power consumption measured
by the power consumption measuring unit 14 to the maximum
power-transmission capability of 3.25 W stored in the power-transmission
capability register 151 immediately after a transfer of 1 packet.

[0087]When the power consumption is less than 3.25 W in the comparison
result, the power-transmission capability monitoring unit 15 controls the
data transfer processing unit 13 to transfer new packet data without
temporarily stopping the transfer, and then performs comparison
processing with the comparing unit 152 mentioned above.

[0088]On the other hand, when the power consumption exceeds 3.25 W, the
power-transmission capability monitoring unit 15 temporarily stops the
packet data transfer to decrease power load, thus decreasing power
consumption of the whole of the removable media control apparatus 1.
After that, when the power-transmission capability monitoring unit 15
confirms that the power consumption is 3.00 W or less which is one stage
lower than 3.25 W during the temporary stop, the power-transmission
capability monitoring unit 15 controls the data transfer processing unit
13 to restart the transfer processing of new packet data. Immediately
after that, the power-transmission capability monitoring unit 15
continuously performs similar comparison processing.

[0089]The power consumption exceeds the maximum power-transmission
capability for about 1 μsecond in FIG. 9A. However, the removable
media control apparatus 1 usually includes a charging circuit such as a
capacitor therein, so that the removable media control apparatus 1 can
keep its operation stable even in a temporary supply-power shortage and
can transit to an operation of the temporary stop.

[0090]By repeating the above operations, the removable media control
apparatus 1 can perform the data transfer in accordance with the upper
limit of the power-transmission capability register 151.

[0091]Here, the power-transmission capability monitoring unit 15
preliminarily parameterizes a relationship between power consumption and
the number of packets which can be continuously transferred and stores
the parameter in the power-transmission capability register 151 thereof.
Accordingly, the power-transmission capability monitoring unit 15 can
regularly generate a temporary-stop period and thus control the power
consumption in the data transfer.

[0092]Further, though the transfer processing is temporarily stopped when
the power consumption is about to exceed 3.25 W in the above processing,
the removable media control apparatus 1 may control its operation at
three separate ranges as the following description.

[0093]For example, the removable media control apparatus 1 sets a "first
range" which is less than 3.00 W, a "second range" which is from 3.00 W
to less than 3.25 W, and a "third range" which is 3.25 W or more. Then,
in a case of the first range, the removable media control apparatus 1
performs data transfer at a large transfer size unit with the data
transfer processing unit 13. In a case of the second range, the removable
media control apparatus 1 performs data transfer at a small-divided
transfer size with the data transfer processing unit 13 so as to decrease
average power consumption. Further, the removable media control apparatus
1 performs a power-saving operation in non-transfer period. In a case of
the third range, the removable media control apparatus 1 suspends the
data transfer before bus power interruption operation at a host device 2
side is carried out so as to perform error notification to the host
device 2 through the data-transmission line 21.

[0094]As above, the removable media control apparatus 1 controls the data
transfer speed between the host device 2 and the removable media 3 so as
to prevent power consumption measured by the power consumption measuring
unit 14 from exceeding the maximum power-transmission power stored in the
power-transmission capability register 151. Thus, the removable media
control apparatus 1 controls the data transfer speed between the host
device 2 and the removable media 3, being able to perform the data
transfer at high speed while preventing the power consumption from
exceeding the maximum power-transmission power.

[0095]The present application contains subject matter related to that
disclosed in Japanese Priority Patent Application JP 2009-222844 filed in
the Japan Patent Office on Sep. 28, 2009, the entire content of which is
hereby incorporated by reference.

[0096]It should be understood by those skilled in the art that various
modifications, combinations, sub-combinations and alterations may occur
depending on design requirements and other factors insofar as they are
within the scope of the appended claims or the equivalents thereof.